Overview
CVE-2017-0249 describes an elevation of privilege vulnerability in ASP.NET Core caused by improper sanitization of web requests (CWE-20: Incorrect Input Validation). In real-world terms, such flaws can allow attackers who craft malicious requests to influence authorization decisions and access sensitive data they should not reach. This guide references CVE-2017-0249 to illustrate how insufficient input validation can enable privilege escalation and potential data exposure in ASP.NET Core applications.
Code Fix Example
ASP.NET Core API Security Remediation
Vulnerable pattern:\nusing System.Collections.Generic;\nusing System.Security.Claims;\nusing Microsoft.AspNetCore.Mvc;\n\n[ApiController]\n[Route(\"api/[controller]\")]\npublic class DataController : ControllerBase\n{\n [HttpGet]\n public IActionResult Get(string role)\n {\n // Vulnerable: trusts client-provided role to grant access\n var claims = new List<Claim>\n {\n new Claim(ClaimTypes.Name, \"attacker\"),\n new Claim(ClaimTypes.Role, role)\n };\n HttpContext.User = new ClaimsPrincipal(new ClaimsIdentity(claims, \"Vulnerable\"));\n if (HttpContext.User.IsInRole(\"Admin\"))\n {\n return Ok(\"Sensitive data: secret-table-42\");\n }\n return Forbid();\n }\n}\n\nFixed pattern:\nusing Microsoft.AspNetCore.Authorization;\nusing Microsoft.AspNetCore.Mvc;\n\n[ApiController]\n[Route(\"api/[controller]\")]\npublic class DataControllerFixed : ControllerBase\n{\n [HttpGet]\n [Authorize(Roles = \"Admin\")]\n public IActionResult Get()\n {\n return Ok(\"Sensitive data: secret-table-42\");\n }\n}